The present application relates to an optical shutter for a display device, an image display apparatus including the optical shutter, and an apparatus and method for manufacturing the optical shutter. In particular, the present application relates to an optical shutter for a display device, the optical shutter being capable of operating at high speed and providing improved light extraction efficiency, to an image display apparatus including the optical shutter, and to an apparatus and method for manufacturing the optical shutter.
There have been studied various techniques that relate to optical shutters for a display device. For example, for improvement of optical shutters with liquid crystal, angles of liquid crystal particles with respect to an absorption axis of a polarizer are modified (e.g., see Japanese Unexamined Patent Application Publication No. 2005-284261), techniques for application of an electric field (e.g., see Japanese Unexamined Patent Application Publications Nos. 2003-262847 and 2002-131717) and alignment processing (e.g., see Japanese Unexamined Patent Application Publication No. 2002-148625) are developed, and asperities are formed on a substrate surface (e.g., see Japanese Unexamined Patent Application Publication No. 2000-347171). However, because of the principle of a liquid crystal display device, a polarizer is used in each case. Therefore, the amount of light actually extracted is as small as several percent of the amount of light of a light source (i.e., light extraction efficiency is low). Additionally, the response speed of liquid crystal display devices currently available are as low as about five milliseconds.
On the other hand, there is a method in which electrowetting technology is used for display on a display device. For example, a liquid device containing liquid is used as an optical shutter for light to be output from a light source (light emitter). The liquid device includes at least one type of polar liquid, at least one type of nonpolar liquid, an insulating film, and electrodes. In the liquid device, application of an electric field changes wettability (surface tension) between the insulating film and the polar liquid. This technique (electrowetting) makes it possible to change the contact angle of the nonpolar liquid with respect to the insulating film. In other words, it is possible to change the curvature radius of the surface of the nonpolar liquid without changing the volume of the nonpolar liquid. At the same time, if a black dye which does not allow light to pass through is dissolved in either one of the polar liquid and the nonpolar liquid, light can be alternately transmitted or blocked by varying the voltage.
Unlike a conventional optical shutter, such a liquid device does not require a polarizing filter or the like. Therefore, the efficiency of light extraction in the liquid device is much higher than that in the conventional optical shutter.
However, optical shutters for a display device are typically expected to provide higher brightness and operate at higher speed. For an optical shutter to which the above-described electrowetting is applied, the amount of oil filled in pixels is not disclosed in detail. The response speed of such an optical shutter is as low as 0.1 millisecond, which needs to be higher. Additionally, the drive voltage corresponding to this response speed is as extremely high as 30 V or above, which needs to be lower.
The present application has been made in view of the circumstances described above. It is desirable to achieve high-speed and low-voltage operation and improve light extraction efficiency.